In a conventional stator, a stator core is made of stacked steel plates. An insulator is embedded in the stator core. The insulator is an insulator made of a synthetic resin. The annular stator core is formed with tooth portions protruding in a diametrically inward direction at a plurality of points at which an inner periphery thereof is equally divided in a circumferential direction. Wire materials are wound around the respective tooth portions through the insulator, so that a plurality of layers of windings is formed. In the wire materials configuring the winding, one layer of the innermost side is an aluminum wire, and other five layers of the outer sides are copper wires (refer to Patent Document 1).
In another conventional stator, an insulator is disposed in a stator slot of a stator iron core. Main windings are accommodated at an inner side of the insulator. The main windings are formed by winding main magnet wires into an irregular winding. The number of the magnet wires is 34 wires, for example. Auxiliary windings are accommodated in spaces formed between the adjacent main windings. The auxiliary windings are formed by winding auxiliary magnet wires by the same number as the main windings. A wire diameter of the auxiliary magnet wire is 154/1000 of the main magnet wire.
In another conventional stator, aluminum is used for the auxiliary magnet wire forming the auxiliary windings. Copper is used for the magnet wire of the main windings (refer to Patent Document 2).